Our work has focused on bringing retroviral gene transfer techniques developed in the Hematology Branch into clinical applications targeting human hematopoietic progenitor and stem cells. Over the past year we have enrolled a total of 17 patients undergoing autologous stem cell transplantation for aggressive treatment of breast cancer or multiple myeloma into clinical retroviral genetic marking trials. These trials were designed to answer important questions regarding the feasibility of using retroviral vectors to transfer genes into human hematopoeitic stem and progenitor cells, the potential for using bone marrow versus peripheral blood stem and progenitor cells as targets for gene therapy, the pattern and durability of engraftment with bone marrow versus peripheral blood grafts after transplantation, and the source of relapse after aulogous trnasplnatation for these malignancies. 14/17 patients analyzed thus far post-transplant show evidence of hematopoietic cells containing the transferred gene. 5 patients continue to show the presence of the marker gene at one year after transplantation. The level of marked cells is very low, and we are modifiying the techniques used to get vector into the target stem cell to try and increase efficiency. No adverse events related to the gene transfer procedure have been observed. In preclinical in vitro and animal models we are exploring the use of serum-free transduction systems and concentrated, purified viral vectors to try and increase efficiency of gene transfer. We have shown that transduction can occur in a serum -free environment using highly purified vector preparations. We are also attempting to block cytokine inhibition of primitive cell cycling to allow better transduction. Based on the data we are generating in the clinical marking trials andents and murine and primate animal data, we have embarked on two potentially therapeutic protocols: transfer of the multidrug-resistance gene to autologous marrow to confer chemoprotection in breast cancer patients, and transfer of the glucocerebrocidase gene to bone marrow or peripheral blood stem cells to treat Gaucher Disease.